Elastomeric composition of neoprene, polyether polyprimary polyamine and a basic curing agent

ABSTRACT

Curable elastomeric compositions comprising neoprene, at least one neoprene curing agent, and a polyether polyprimary polyamine having a polyether moiety containing recurring oxyalkylene groups in which the alkylene has from two to six carbon atoms, said polyether polyprimary polyamine having a molecular weight of at least about 3500 and cured products obtained therefrom.

United States Patent [191 Jonnes [54] ELASTOMERIC COMPOSITION OF NEOPRENE, POLY ETHER POLYPRIMARY POLYAMINE AND A BASIC CURING AGENT [75] Inventor:

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Nov. 2,1970 [21] Appl. No.: 86,285

Nelson Jonnes, Stillwater, Minn.

[52] U.S. Cl. 260/415 A, 260/4l.5 R, 260/836,

' 260/837 R, 260/890 [51] Int. Cl. ..C08d 9/10 [58] Field of Search .260/890, 836, 4 l .5

[56] References Cited 9 UNITED STATES PATENTS 3,459,694 Bowman ..260/23.7

[ 1 Jan. 30, 1973 3,436,359 4/1969 Hubin et al ..260/2 3,373,123 3/l968 Brice ..260/2.5 3,308,204 3/1967 Bugel ..260/837 Primary ExamineP-Murray Tillman Assistant ExaminerJohn Seibert Att0rneyKinney, Alexander, Sell, Steldt & Delahunt [5 7] ABSTRACT 12 Claims, No Drawings v ELASTOMERIC COMPOSITION OF NEOPRENE, POLYETHER POLYPRIMARY POLYAMINE AND A BASIC CURING AGENT This invention relates to novel curable elastomeric compositions which can be cured to elastomers having a good balance of physical properties.

Among the many elastomers commercially available neoprene is known to possess excellent mechanical properties, although it has generally only a moderate resistance to abrasion and limited tear strength and therefore is not suitable for many applications, even if the neoprene is appropriately compounded with reinforcing fillers.

It has now been found that polyether polyprimary polyamines may be admixed with neoprene in the presence of a neoprene curing system, preferably with a reinforcing pigment, to provide a composition which can be cured to an elastomer having surprisingly good combination of resistance to abrasion and resistance to tear, together with other desirable properties, such as tensile strength, elongation and hardness, which are of value in a tough rubber. Within the scope of this invention a significant improvement in tear strength of neoprene can be achieved without sacrifice of other desirable elastomeric properties. These curable compositions may be formulated with sufficient solvent to provide a composition which can be'coated or cast prior to curing and which can serve as an adhesive for bonding a variety of surfaces, e.g. neoprene, metal, plastics, wood, ceramics and glass. The composition of this invention may also be formulated with little or no solvent to provide a'rubber base stock which can be milled on a conventional rubber mill and cured to form a useful elastomer, following the general procedures in the rubber industry.

Any of the various types of neoprene can be used, including the sulfur-modified (types GN, GNA and GRT) and the non-sulfur modified varieties (types W and WRT). The sulfur modified types are prepared by interpolymerization with sulfur and generally contain thiuram disulfide stabilizers. The different types of neoprenes, neoprene curing systems and their processing are described in The Neoprenes, by RM. Murray and DD. Thompson E.I.DuPont DeNemours, Wilmington, Del. (1963).

The polyether polyprimarypolyamines of this invention have a polyether moiety composed of recurring oxyalkylene groups in which the alkylene radical has from two to six carbon atoms, the molecular weight being at least 3500, generally between about 4,000 and 20,000, preferably from 5000to 15,000 because those with molecular weights above 20,000 are more difficult to process and do not normally provide optimum properties in the cured product. It is desirable to use polyether polyamines with a high degree of terminal amine functionality, such as at least 70%, preferably at least 90 percent, of theoretical (i.e. in the theoretical limit all terminal groups are primary amino groups), since polyethers with only one terminal amino group serve primarily as plasticizers in the formulation. Most preferred are the polyether polyprimary polyamines of U.S. Pat. No. 3,436,359, which have a high primary amine functionality, i.e. at least 90 percent primary amine terminal groups. Such preferred polyether polyamines have molecular weights of at least 3,500 and have terminal primary amino groups attached directly to each end of a polyether moiety containing recurring groups of which at least a major portion consists of oxytetramethylene recurring units and at most a minor portion consists of another oxyalkylene or thioalkylene recurring units having from two to six straight chain carbon atoms, at least half of the primary amino terminal groups having the structure OC,,I'I Nl-l the polyether moiety having less than about 3 percent by weight of secondary amino nitrogen atoms and less than about 0.3 percent by weight of tertiary amino nitrogen atoms in its essentially linear chain.

The neoprene curing system can be of two general types. In the first type, the curing system comprises an organic base having a base strength at least that of benzylamine, especially an aliphatic amine (including the salts thereof, such as the carbamate salts) e.g. hexamethylenediamine, benzyldimethylamine, tris(dimethylaminomethyl)-phenol, dicyandiamide, etc. The second type of curing system is used when the composition contains epoxy compound having an oxirane equivalence greater than 1, preferably about 1.5 to 2.2, oxirane equivalence being defined as the number of oxirane equivalents per molecule. To avoid excessive hardness, the oxirane/amine equivalence ratio is preferably no more than about 25, the oxirane/amine equivalence being defined as the number of oxirane equivalents present in the total weight of epoxy resin divided by the number of amine-attached, active hydrogen equivalents present in the total weight of the polyether polyprimary polyamine. Monoepoxides act as plasticizers but do not contribute directly to the tear strength of the cured product. Since the aliphatic polyepoxides are not as effective in providing the improved tear strength, the epoxy resins containing some aromaticity are particularly preferred. Included in this preferred category are the epoxy compounds derived from diglycidyl ethers of polyphenols, such as 2,2-bis(parahydroxy phenyl) propane (also known as bis-phenol A). Epoxy-amine reaction catalysts, such as the soluble metal salts of organic acids, e.g. salts of metals in groups IIB, [VB and VII of the Periodic Table, may be used with the epoxy compounds to further improve the product, particularly such salts as stannous octoate, cobalt naphthenate, zinc acetate, stannous oleate, dibutyl tin dilaurate. This second type of curing system includes inorganic metal oxide bases, e.g. zinc oxide, magnesium oxide, etc. and/or organic bases having a base strength at least that of benzylamine, as described earlier.

Other additives may be included in conventional manner to improve processability and/or to improve the processability and/or to improve the physical properties of the cured products, such as processing aids, antioxidants, plasticizers, pigments, weakly basic amines (e.g. methylene dianiline), and low molecular weight polyether diamines, even though such amines may occasionally decrease the scorch resistance of the fonnulation. Reinforcing pigments are generally most advantageous to obtain maximum tear strength, and at least about 25 parts by weight (e.g. 60-180 parts) of a reinforcing pigment, such as silica, carbon black, titanium dioxide, talc, etc. based on parts by weight of neoprene, is therefore preferred, the upper limit being determined primarily by the particular use of the composition. For example, less reinforcing filler is normally present for adhesive use. Silica is particularly preferred when the composition is intended for molded products as compared to the solution formulations used for adhesives and coatings.

Useful elastomeric products are provided with a wide variation in the relative quantities of the several components. The ratio of polyether polyprimary polyamine to the neoprene generally ranges from 1:20 to :1, preferably from 1:10 to 2:1 in the absence of an epoxy compound and from 1:4 to 5:1 in the presence of an epoxy compound. The neoprene curing agents are included in quantities conventional for neoprene curing, or even in slightly larger quantities.

Because of the unusual combination of abrasion resistance, strength, elongation at break and tensile at break, these products are tough rubbers which are particularly suitable for extreme duty use, such as in solid tires or tread stock for forklift trucks and off-the-road vehicles, die cutter bed coverings, O-rings, shaft seals, gaskets, clutch facings, capstan rollers and the like.

EXAMPLE 1 A coating solution was prepared by mixing and then milling on a three roll paint mill the following ingredients:

Parts by Wt. polytetramethylene oxide diprimary dlamine solution (MW=10,000)(50% in toluene) I00 tris(dimethylaminomethyl) phenol 2.0 carbon black 13.24 diglycidyl ether of bis-phenol A (epoxy equiv.wt.=190) 20.00 S-aminopropyl-trimethoxysilane 2.81 silicone oil (DC200", a trademarked product of Dow Corning Company) 1.40 neoprene curing system magnesium oxide 0.38 stearic acid 0.05 zinc oxide 0.48 2,2'-methy1enebis-(4-methy1-6- -tert.-buty1) phenol 0.19 ethylene thiourea 0.05

neoprene W solution (20% in toluene) The neoprene solution was prepared from unmilled gum stock. The above formulation was coated onto a release carrier paper using a coating bar set with a 25 mil clearance. The film was allowed to dry and then was cured at room temperature for 48 hours. The dry film thickness was 10.3 mils. This film had a tensile strength of 2,300 psi on a one-quarter inch wide sample, as compared to 1,800 psi on a similar sample prepared without the neoprene solution and the neoprene curing agents, and the neoprene containing sample was tougher and significantly higher in tear strength at 340F. This film can be used as a protective coating, particularly for rubber goods which otherwise are subject to attack by ozone.

EXAMPLE 2 The following three solutions were prepared:

Parts by wt. Part A polytetramethylene oxide diprimary diamine (MW=10,000) 100 carbon black I 40 2,4,6-tri(dimethylaminomethy1)phenol 7 toluene 103 Part B polymerized diglycidyl ether of bis-phenol A (epoxy eq.wt.=190) 65 toluene 53.5 Part C neoprene Type \V 58.4 magnesium oxide 2.3 carbon black 1 1.0 stearic acid 0.3 zinc oxide 2.9 toluene 224.7

Part A was prepared by first mixing all ingredients with a high speed mixer and the milling for two passes on three r011 paint mill. Following the milling, toluene was added to adjust the solids to 58.8 percent. Part C was prepared by milling on a two roll rubber mill all of the ingredients except the solvent. Following the milling, the rubber was chopped, placed in the solvent and churned for 2 days, at which time it was completely dissolved.

Sample solutions were prepared by mixing Part A solution (247 grams) and Part B solution (118.5 grams) and adding varying amounts of Part C solution to provide varying amounts of neoprenein the samples. After mixing the ingredients with a propeller type mixer for several minutes, the solutions were allowed to deaerate and were then used as a protective rubber coating. Test samples were prepared by coating the solution onto a release paper carrier, drying at room temperature for one week and then testing the physical properties. Test results are shown below. Tear strengths were measured as pounds per lineal inch on standard tensile test equipment (Instron) using Die C,

several specimens being tested and reported for each sample.

Wt.% neoprene based on Percent Tensile Tear Sample total solids Elongation psi Strength It is apparent that an improvement in tear strength is realized in samples (b) through (h), as compared to the value calculated on an additive basis from samples (a) and (i).

EXAMPLES (TABLES 1 AND 11) ternately as required for easy handling of the batch. and samples 9 and were press cured at 320F. for 20 Finally, any catalysts such as stannous octoate and orminutes. In Table [I samples l3-25 were press cured at ganic amine'are incorporated before the batch was 320-340F. for 30 minutes, samples 18-20 and 23-25 removed from the mill and molded. This procedure was being subsequently post cured at 350F. for 30 minutes. used for the examples set forth in Tables I and 11. In 5 Sample ll was centrifugally cast at 220F. for 120 each occurrence the polyether moiety of the polyether minutes. Sample ll was press cured at 320F. for 20 diprimary diamines and the polyether dlsecondary minutes.

TABLE I Neoprene (Type KNR) 100 Neoprene (Type WB) 100 100 100 100 100 100 100 100 Neoprene (Type WRT)... Colloidal silica 80 80 80 80 80 80 80 Zinc oxdie- 5 5 5 Magnesium 0Xld0.. 4 4 4 Ethylene thiourea 0.5 0.5 0. 5 Dioetyl sebacate 5 5 5 Zme stearate.. 5 5 5 Antioxidant 1 1 1 1 HzN (C4Hg0) DC H11NH1(10,000 molecular Weight) 25 75 25 25 50 Stannous octoate 13 13 2,4,6,-tri (dimethylaminom ethyl) phenoL 3 3 3 Tear strength (lb./in. thickness) 227 460 Shore A hardness 76 76 Tensile at break (p.s.i.) 1, 529 2, 752 Elongation at break (percent) 140 Permanent set (percent). 7 l5 1 100% modulus (p.51) 1,072 434 323 227 389 288 305 256 196 218 300% modulus (p.s.i.) 1, 675 1, 306 1, 543 1, 055 569 588 518 439 62/1 'ils'ii'iiE It 11 12 1s 14 15 10 17 1s 19 20 21 22 23 24 25 Neoprene (Type GRT) 100 100 100 Neoprene (Type S) Neoprene (Type WD) Neoprene (Type WRT) Tetramethyl thluram monosulfid Ortho tolyl guanidine. Colloidal silica.-.

Zinc 0x1 0 Iron oxi 100 Polyether diprimary diamine (MW-10,000) 100 100 100 300 100 100 100 100 100 100 100 Stannous oetoate 15 24 12 24 72 24 12 12 12 24 24 2,4,6-tri(dimethylaminomethyl) phenol 2.5 5 2.5 5 15 5 2. 5 5 5 Epoxy resin (epoxy equiv.

W12- 19 50 50 25 50 150 50 50 25 25 50 50 Epoxy resin (epoxy equiv.

Wt. 1,000) 50 Dicyandiamide 0.8 0.8 Epoxy resin (epoxy equiv.

wt. 500) 25 25 Tear strength (#1111. thickness)- 255 585 609 686 692 519 322 628 577 595 265 203 283 688 792 Shore A hardness 64 69 82 80 79 77 71 78 77 83 94 84 73 75 Tensile at break (p.s.i.) 5, 500 3,100 2, 931 2,865 2,773 2, 557 2, 547 2,272 2,730 2,681 2,378 1, 310 013 3,243 3,450 Elongation at break (percent) 590 670 600 640 520 645 692 590 445 400 200 740 100 380 480 Permanent set (percent) 15 28 18 25 22 20 29 18 8 3 12 72 9 0 6 100% modulus (p.s.i.) 300 500 543 566 555 471 303 584 520 980 1, 612 398 609 585 300% modulus (11.51.) 1, 688 1, 531 1, 307 1, 369 1, 074 1,688 2, 035 2,170 710 2,617 2, 660

"iqnphthonic. oil with 01111 no point of 156 F. (69 (3.).

diamines was polyoxytetramethylene. Examples 1, w i l i d i 5-1 1 22 and 23 in Tables I and ll (10 not fall Within the 1, curable elastomenc compos t ons compnsmg pr mventlofl and a pr n y for neoprene, at least one neoprene curing agent selected parison. All epoxy resin in Tables 1 and II are derived from the group consisting of an aliphatic amine base from diglycidyl ether of bis-phenol A. The variations in having a base strength at least that of benzylamine and curing conditions among certain of the examples do not a basic inorganic metal oxide, and a polyether polyprichange the comparative value of the results. in Table 1 mary polyamine having a polyether moiety containing samples l-8 were press cured at 320F. for 15 minutes recurring oxyalkylene groups in which the alkylene has from two to six carbon atoms, said polyether polyprimary polyamine having a molecular weight of at least about 3,500.

2. The curable elastomeric composition of claim 1 in which said neoprene curing agent comprises an aliphatic amine base having a base strength at least that of benzylamine.

3. The curable elastomeric composition of claim 1 in which said composition also comprises at least one epoxy compound having an oxirane equivalence greater than 1. q

4. The curable elastomeric composition of claim 1 in which said composition contains at least 25 parts by weight of a reinforcing pigment per 100 parts of neoprene.

5. The curable elastomeric composition of claim 4 in which said reinforcing pigment is silica.

6. The curable composition of claim 1 in which the ratio of said polyether polyprimary polyamine to said neoprene is from about 1:20 to about 10:1.

7. The curable composition of claim 6 in which the ratio of said polyether polyprimary polyamine to said neoprene is from about 1:10 to about 2:1 or, when an epoxy compound having an oxirane equivalence greater than 1 is present, from about 1:4 to about :1.

9. An abrasion and tear resistant elastomer prepared I by curing a mixture comprising neoprene and a polyether polyprimary polyamine having a molecular weight of at least 3,500 and a polyether moiety containing recurring oxyalkylene groups in which the alkylene has from two to six carbon atoms in the presence of at least one aliphatic amine base having a base strength at least that of benzylamine or a basic inorganic metal oxide.

10. The abrasion and tear resistant elastomer of claim 9 in which at least a major portion of the oxyalkylene recurring groups in said polyether polyprimary polyamine are oxytetramethylene groups.

11. The abrasion and tear resistant elastomer of claim 10 in which said mixture also contains an epoxy compound having an oxirane equivalence greater than one.

12. The curable elastomeric composition of claim 3 in which at least a major portion of the oxyalkylene recurring groups in said polyetherpolyprimary polyamineare oxytetra-methylene groups.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3,71 i,115

DATED 1 January 30, 1973 |NVENTOR(S) 1 Nelson Jonnes it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 5 and 6, Table I, line 2: "Neoprene (Type WB)" should read neoprene (Type WD) Column i, line 9, after word "and", the word "the" should read then Signed and sealed this 13th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

1. Curable elastomeric compositions comprising neoprene, at least one neoprene curing agent selected from the group consisting of an aliphatic amine base having a base strength at least that of benzylamine and a basic inorganic metal oxide, and a polyether polyprimary polyamine having a polyether moiety containing recurring oxyalkylene groups in which the alkylene has from two to six carbon atoms, said polyether polyprimary polyamine having a molecular weight of at least about 3,500.
 2. THe curable elastomeric composition of claim 1 in which said neoprene curing agent comprises an aliphatic amine base having a base strength at least that of benzylamine.
 3. The curable elastomeric composition of claim 1 in which said composition also comprises at least one epoxy compound having an oxirane equivalence greater than
 1. 4. The curable elastomeric composition of claim 1 in which said composition contains at least 25 parts by weight of a reinforcing pigment per 100 parts of neoprene.
 5. The curable elastomeric composition of claim 4 in which said reinforcing pigment is silica.
 6. The curable composition of claim 1 in which the ratio of said polyether polyprimary polyamine to said neoprene is from about 1: 20 to about 10:1.
 7. The curable composition of claim 6 in which the ratio of said polyether polyprimary polyamine to said neoprene is from about 1: 10 to about 2:1 or, when an epoxy compound having an oxirane equivalence greater than 1 is present, from about 1:4 to about 5:
 1. 8. The curable composition of claim 1 in which said polyether polyprimary polyamine is a polyether diprimary diamine having at least 90% of the theoretical primary amino termination.
 9. An abrasion and tear resistant elastomer prepared by curing a mixture comprising neoprene and a polyether polyprimary polyamine having a molecular weight of at least 3,500 and a polyether moiety containing recurring oxyalkylene groups in which the alkylene has from two to six carbon atoms in the presence of at least one aliphatic amine base having a base strength at least that of benzylamine or a basic inorganic metal oxide.
 10. The abrasion and tear resistant elastomer of claim 9 in which at least a major portion of the oxyalkylene recurring groups in said polyether polyprimary polyamine are oxytetramethylene groups.
 11. The abrasion and tear resistant elastomer of claim 10 in which said mixture also contains an epoxy compound having an oxirane equivalence greater than one. 